Tube furnace for thermal decomposition process

ABSTRACT

A tube furnace for a thermal decomposition reaction in which a fluid traverses a multiplicity of parallel tubes extending through a housing, a plurality of thermal radiating webs being interposed between the tubes to prevent them from casting radiation shadows upon one another and creating non-uniformly heated tube walls.

0 United States Patent 1191 p 1111 3,863,607 Kreuter Feb. 4, 1975 1 TUBE FURNACE FOR THERMAL 2,752,897 7/1956 Mekler..... 110/98 R DECQMPOSITION PROCESS 3,276,436 10/1966 Guerrieri 122/356 [75] Inventor: Walter Kreuter, Munich, Germany 73 Assignee: linde Aktiengesellschaft, Wiesbaden, Primary Examiner-Edward Favors A Germany Attorney, Agent, or FzrmKar1 F. Ross; Herbert Dubno [22] Filed: Jan. 18, 1974 [21] Appl. No.: 434,570

ABSTRACT [30] Foreign Application Priority Data Jan. 19, 1973 Germany 2302612 A tube furnace for a thermal decomposition reaction in which a fluid traverses a'multiplicity of parallel Cl 3 5 122/367 tubes extending through a housing, a plurality of ther [51] Int. Cl. F2211 21/00 a] radiating webs being interposed between the tubes Field of Search 367 to prevent them from casting radiation shadows upon 110/9 126/91 432/219 one anotherand creating non-uniformly heated tube walls. [56] References Cited UNITED STATES PATENTS Lorenzo 122/356 12 Claims, 2 Drawing Figures Y TUBE FURNACE FOR THERMAL DECOMPOSITION PROCESS FIELD OF THE INVENTION The present invention relates to a tube furnace for thermal decomposition processes of the type in which a multiplicity of tubes, traversed by the medium to be heated, are disposed in a housing which is heated so that the tubes absorb energy at least in part by radiation. More particularly the invention relates to a tube furnace in which nonuniform heating of the tubes or the development of nonuniform temperatures along and around the tube walls are precluded.

BACKGROUND OF THE INVENTION Tube furnaces for carrying out thermal decomposition reactions, gas-phase reactions generally and other processes requiring the application of heat to a medium within the furnace comprises an elongated housing through which a mulitplicity of tubes in one or more rows extend in spaced apart relation. The housing is provided with heat-generating means, e.g. radiation devices or burners, with at least part of the thermal energy being applied to the tube in the form of radiation.

The walls and bottom of the furnace chamber may be provided with burners which heat the chamber and thereby transmit radiant energy to the .plurality of pipes or tubes therein. The tubes which generally run in the vertical direction, are supplied with a decomposable medium which is heated through the tube walls.

Because of the high temperatures which are provided in the radiation chamber, the reactor tubes are locally heated to their upper temperature limits and generally it is desirable to ensure a uniform (constant) heating of the tubes along the tube walls both in the circumferential and in the longitudinal direction.

However, the very presence of other tubes in the array or in the vicinity of each tube interferes with the thermal radiation to any particular tube and in effect causes radiation shadows. These radiation shadows result in nonuniform thermal loading of the tubes with the mechanical disadvantages which have been associated with such nonuniform loading and furthermore cause the tubes, upon which radiation shadows have been cast, to have portions of low temperatures.

Consequently, the residence time of the inactive fluid, i.e., the fluid undergoing decomposition, is longer than is desirable because the fluid encounters locally underheated regions. As a whole, therefore, the throughput of the furnace is limited by the limited specific heat-transfer of the system. The term specific heat-transfer is used to describe the heat received (transferred) per unit surface area of the tube and should be uniform throughout the length and circumference thereof so that a uniform temperature is likewise maintained.

OBJECTS OF THE INVENTION SUMMARY OF THE INVENTION These objects and others which will become more readily apparent hereinafter are attained, in accordance with the present invention, in a system which comprises a housing receiving a multiplicity of furnace tubes, generally of a refractory material such as alumina, means in the furnace for radiantly heating the furnace tubes, and radiating partitions interposed between the tubes. According to the present invention, therefore, the uniform heating of the walls of the furnace tubes is ensured by providing between them radiating surfaces. Consequently, the radiation shadows previously creating a problem in a multi-tube furnace are eliminated.

The radiant surfaces, according to the invention, reach a steady state temperature within the radiation chamber of the furnace and hence are at the temperature of the radiating walls and members thereof so that they can transmit the heat picked up by the radiating partitions by radiation to the reactor tubes along which they are positioned even along the sides of the reactor tubes opposite those along which the burners are disposed. It has been found to be possible, by providing a number of such radiation surfaces around the furnace tubes and. between each pair of tubes to attain a substantially uniform surface heating of the furnace tubes and an approximately constant heat transfer per unit area of the tube walls.

According to another feature of the invention, the radiating surfaces are ignition-resistant foils and/or strips or bands of refractory material. It has been found to be desirable to provide the strips or bands parallel to the tubes and to the generators or axis thereof and perpendicular to common axial planes of pairs of mutually juxtaposed tubes, the width of the strip being a small fraction of the interaxial distance between the tubes but at least equal to the external diameters thereof. The tubes may be exposed at one side to the burners and preferably have a pair of such reflective strips flanking each tube while another pair of such strips include an obtuse angle between them and lies symmetrically at opposite sides of an axial plane through the tube parallel to the flanking strips. An arrangement of this type has been found to give optimum results with respect to radiant heating of the size of the furnace tube turned away from the side juxtaposed with the burners.

The radiation strips, according to the invention, are suspended by springs in the furnace chamber.

BRIEF DESCRIPTION OF THE DRAWING The above and other objects, features and advantages of the present invention will become more readily apparent from the following description, reference being made to the accompanying drawing in which:

FIG. 1 is a transverse cross-sectional view through tube furnace according to the present invention; and

FIG. 2 is a longitudinal section through the furnace, parts of the drawing being shown diagrammatically.

SPECIFIC DESCRIPTION In the drawing, I show a tube furnace which comprises a radiation chamber 1 enclosed by a pair of vertical walls 2 and 3 and another pair of lateral vertical walls one of which is shown at 10 in FIG. 2.

In the walls 2 and 3, burners 4 are mounted in accordance with conventional principles.

The radiation chamber 1 is provided with two rows of furnace tubes 5 of refractory composition, the tubes of the two rows being horizontally offset from one another so that each tube of one row lies between a pair of tubes of the other row as is best seen from FIG. 1. In addition, each array of tubes lies in a vertical plane (perpendicular to the plane of the paper in FIG. 1) parallel to each other. The tubes are of cylindrical configuration and may emerge from the top and bottom 11 and 12 of the furnace as represented in F IG. 2 for connection to a source of the fluid to be decomposed. Between each pair of tubes 5 of each array, there are provided radiation surfaces 6, here constituted as strips whose width W can be greater than the external diameter D of the furnace tube and which lie in a plane perpendicular to the plane P of the axis of the two tubes. The strips 6 are bisected by the plane P.

The strips 6 are equidistant between the tubes 5 between which they are interposed and preferably lie at a distance S from each tube which is greater than the width W. A similar strip is provided between each tube 5 and the closest tubes of the other array.

As will be apparent from FIG. 1, moreover, each tube 5 is flanked by a pair of parallel strips 6 and has its side turned away from the burners 4 shielded by a pair of strips which together form an obtuse angle and lie symmetrically on opposite sides of the burner plan P through the axis of the furnace tube.

As will be apparent from FIG. 2, the strips 6 may be suspended by springs 7 and can have their lower ends guided between leaf springs 8 to permit thermal expansion and contraction of the components of the system.

The radiating surfaces 6 rapidly receive heat from the radiation chamber 1 and reradiate to the juxtaposed sides of the tubes 5. The effect of cool tubes in creating radiation shadows and the effect of one-sided use of the burners are both eliminated and a uniform heat transfer per unit surface area can be achieved at the maximum level. As a result, the residence time of the fluid in the tubes can be reduced and the throughput correspondingly increased.

I claim:

I. A tube furnace comprising a radiation chamber, a multiplicity of furnace tubes in said chamber and in spaced apart relation, heating means in said chamber for heating said tubes,'and radiating surfaces in said chamber disposed along said tubes for absorbing heat from said chambers and reradiating heat to said tubes to maintain the heat transfer per unit surface thereof substantially constant all along and around said tubes, said tubes being disposed in at least two planar and mutually parallel arrays with the tubes of one array being offset with respect to the tubes of the other array by about half the distance between the tubes of each array and each of said tubes is flanked by a pair of said radiating surfaces each extending perpendicular to the plane of the axis of the tubes of the respective array, each of said radiating surfaces being a planar strip of a width at least equal to that of the diameter of the tube disposed midway between a pair of tubes of each array and said radiating surfaces include like strips disposed equidistantly between each tube of one array and a pair of tubes of the other array and perpendicular to common axial plane of the tubes between which the strips are disposed.

2. The tube furnace defined in claim 1 wherein said radiating surfaces are formed as ignition-resistant foils.

3. The tube furnace defined in claim 1 wherein said radiating surfaces are formed as bands of refractory material.

4. The tube furnace defined in claim 1 wherein said 5 radating surfaces extend parallel to said tubes and perpendicular to common axial planes between pairs of tubes.

5. A tube furnace comprising a radiation chamber, a multiplicity of furnace tubes in said chamber and in spaced apart relation, heating means in said chamber for heating said tubes, radiating surfaces in said chamber disposed along said tubes for absorbing heat from said chambers and reradiating heat to said tubes to maintain the heat transfer per unit surface thereof substantially constant all along and around said tubes, and

springs positioning said radiating surfaces in said chamber.

6. The tube furnace defined in claim 5 wherein said tubes are disposed in at least two planar and mutually parallel arrays with the tubes of one array being offset with respect to the tubes of the other array by about half the distance between the tubes of each array and each of said tubes is flanked by a pair of said radiating surfaces each extending perpendicular to the plane of the axis of the tubes of the respective array.

7. The tube furnace defined in claim 6 wherein each of said radiating surfaces is a planar strip disposed midway between a pair of tubes of each array and said radiating surfaces include like strips disposed equidistantly between each tube of one array and a pair of tubes of the other array and perpendicular to common axial plane of the tubes between which the strips are disposed.

8. The tube furnace defined in claim 5 wherein said radiation surfaces are formed as ignition-resistant foils.

9. The tube furnace defined in claim 5 wherein said radiation surfaces are formed as bands of refractory material.

10. A tube furnace comprising a radiation chamber,

a multiplicity of furnace tubes in said chamber and in spaced apart relation, heating means in said chamber for heating said tubes, radiating surfaces in said chamber disposed along said tubes for absorbing heat from said chambers and reradiating heat to said tubes to maintain the heat transfer per unit surface thereof substantially constant all along and around said tubes, said tubes being disposed in at least two planar and-mutually parallel arrays with the tubes of one array being offset with respect to the tubes of the other array by about half the distance between the tubes of each array and each of said tubes is flanked by a pair of said radiating surfaces each extending perpendicular to the plane of the axis of the tubes of the respective array, each of said radiating surfaces being a planar strip disposed midway between a pair of tubes of each array and said radiating surfaces include like strips disposed equidistantly between each tube of one array and a pair of tubes of the other array and perpendicular to common axial plane of the tubes between which the strips are disposed, and spring means mounting each of said strips in said furnace.

11. The tube furnace defined in claim 10 wherein said strips each have a width at least equal to the outer diameter of said tubes.

12. The tube furnace defined in claim 11 wherein each of said strips is spaced from a juxtaposed tube by a distance greater than its width. 

1. A tube furnace comprising a radiation chamber, a multiplicity of furnace tubes in said chamber and in spaced apart relation, heating means in said chamber for heating said tubes, and radiating surfaces in said chamber disposed along said tubes for absorbing heat from said chambers and reradiating heat to said tubes to maintain the heat transfer per unit surface thereof substantially constant all along and around said tubes, said tubes being disposed in at least two planar and mutually parallel arrays with the tubes of one array being offset with respect to the tubes of the other array by about half the distance between the tubes of each array and each of said tubes is flanked by a pair of said radiating surfaces each extending perpendicular to the plane of the axis of the tubes of the respective array, each of said radiating surfaces being a planar strip of a width at least equal to that of the diameter of the tube disposed midway between a pair of tubes of each array and said radiating surfaces include like strips disposed equidistantly between each tube of one array and a pair of tubes of the other array and perpendicular to common axial plane of the tubes between which the strips are disposed.
 2. The tube furnace defined in claim 1 wherein said radiating surfaces are formed as ignition-resistant foils.
 3. The tube furnace defined in claim 1 wherein said radiating surfaces are formed as bands of refractory material.
 4. The tube furnace defined in claim 1 wherein said radating surfaces extend parallel to said tubes and perpendicular to common axial planes between pairs of tubes.
 5. A tube furnace comprising a radiation chamber, a multiplicity of furnace tubes in said chamber and in spaced apart relation, heating means in said chamber for heating said tubes, radiating surfaces in said chamber disposed along said tubes for absorbing heat from said chambers and reradiating heat to said tubes to maintain the heat transfer per unit surface thereof substantially constant all along and around said tubes, and springs positioning said radiating surfaces in said chamber.
 6. The tube furnace defined in claim 5 wherein said tubes are disposed in at least two planar and mutually parallel arrays with the tubes of one array being offset with respect to the tubes of the other array by about half the distance between the tubes of each array and each of said tubes is flanked by a pair of said radiating surfaces each extending perpendicular to the plane of the axis of the tubes of the respective array.
 7. The tube furnace defined in claim 6 wherein each of said Radiating surfaces is a planar strip disposed midway between a pair of tubes of each array and said radiating surfaces include like strips disposed equidistantly between each tube of one array and a pair of tubes of the other array and perpendicular to common axial plane of the tubes between which the strips are disposed.
 8. The tube furnace defined in claim 5 wherein said radiation surfaces are formed as ignition-resistant foils.
 9. The tube furnace defined in claim 5 wherein said radiation surfaces are formed as bands of refractory material.
 10. A tube furnace comprising a radiation chamber, a multiplicity of furnace tubes in said chamber and in spaced apart relation, heating means in said chamber for heating said tubes, radiating surfaces in said chamber disposed along said tubes for absorbing heat from said chambers and reradiating heat to said tubes to maintain the heat transfer per unit surface thereof substantially constant all along and around said tubes, said tubes being disposed in at least two planar and mutually parallel arrays with the tubes of one array being offset with respect to the tubes of the other array by about half the distance between the tubes of each array and each of said tubes is flanked by a pair of said radiating surfaces each extending perpendicular to the plane of the axis of the tubes of the respective array, each of said radiating surfaces being a planar strip disposed midway between a pair of tubes of each array and said radiating surfaces include like strips disposed equidistantly between each tube of one array and a pair of tubes of the other array and perpendicular to common axial plane of the tubes between which the strips are disposed, and spring means mounting each of said strips in said furnace.
 11. The tube furnace defined in claim 10 wherein said strips each have a width at least equal to the outer diameter of said tubes.
 12. The tube furnace defined in claim 11 wherein each of said strips is spaced from a juxtaposed tube by a distance greater than its width. 